In the wake of May’s European E. coli outbreak, microbiologists worldwide have sped up efforts to prevent a similar disaster from happening again. Among them, a team of collaborators from universities in the U.S. and Canada may be on the trail of a tiny protein that could render E. coli and other pathogens weak against our inherent defense: human digestion.
A new study published in July’s edition of Microbiology focuses on a novel peptide — a protein too small to merit the title. Known as wrwycr, it has proven to disrupt E. coli bacteria’s natural ability to repair its DNA after damage from stomach acid.
Early lab tests show that after contact with this peptide, Shiga toxin-producing strains of E. coli die off in stomach acid faster than is necessary to enter human intestines, where they cause the medical complications associated with the toxin. Non-Shiga toxin producing E. coli suffer similar fates, but pose little concern in comparison.
Though the team is far from achieving its ultimate goals, the big idea is to use this peptide in a spray or wash for fruits and vegetables, essentially weakening potential pathogens before anyone even chomps into the produce. So far, they’ve only completed the initial tests to prove the theory might work.
“We exposed pathogenic E. coli to this peptide for five minutes at room temperature — and of course compared them to bacteria that had not seen the peptide. The results were profound,” said Debora Foster, Ph.D., cellular biology professor at Ryerson University and the study’s lead author. “We were seeing dramatic differences in the survival rates after acid treatment.”
Along with Dr. Anca Segall from San Diego State University and Dr. Steve Goodman from the University of Southern California, Foster’s team tested the survivability of several E. coli strains — including the well-known O157:H7 — in acid with and without the peptide.
Without it, large, viable numbers of bacteria still survived in the acid after many hours — long enough to move on to colonize the intestines. A meal will typically pass through the stomach over 4 to 5 hours.
But after exposing O157:H7 bacteria to the peptide, the team couldn’t detect any E. coli after as little as 30 minutes in the acid.
The survival rates of other strains varied, but each dropped significantly when exposed to the peptide, Foster said. The team members have not been able to test E. coli O104:H4, the strain behind the European outbreak, but they hope to receive a sample soon.
“This is a long, long way from happening, but our thought was that if we can incorporate this into a spray, we could prevent the bug from ever getting past the stomach,” Foster said. “Many more studies will be needed, but we believe this is a non-toxic, innocuous peptide –simply like eating a small piece of protein.”
Innocuous or not, the peptide is not one humans normally digest. As Foster explained, humans digest proteins made from L-amino acids, while this peptide is composed of D-amino acids. It’s still possible that the peptide could break down after ingestion and serve no help in preventing E. coli from repairing itself during acid stress.
Thus far, the researchers have tested the peptide for toxicity on mammalian cells in culture and saw no effect. The next step will involve animal testing.
Originally, the team was also concerned about the potential release of large Shiga toxin doses upon the bacteria’s destruction in the stomach. Antibiotics are not used on patients infected with E. coli because attacking the bacteria causes the release of potentially lethal amounts of toxin. According to Foster, however, their tests showed no signs of increased toxin production after introducing the peptide.
The team is now proceeding to test the peptide on other pathogens, most notably Salmonella. Foster said the peptide should have roughly the same effect on a variety of bacteria, not just E. coli specifically.
This means the peptide could compromise ingestion of helpful bacteria along the way, but Foster said killing other bacteria is not a concern. The vast majority of helpful bacteria have permanently colonized the intestinal tract where the peptide won’t reach and where no stomach acid could cause harm. Plus, the peptide won’t survive in stomachs for long and only inhibits bacteria that it accompanies there.
Next, Foster hopes to expand the study to more strains of E. coli — particularly O104:H4 –and create an infection model. She knows her team could be working toward the creation of a monumental measure in preventing foodborne illness, but remains conservative in her projections.
“Am I excited? Yes. Do I think there’s real promise here? Yes. But remember: I don’t think the solution will be one strategy. If you look at what other researchers are doing, you’ll see they’re taking a number of different prevention and treatment strategies, and that’s a very good thing,” she said. “I think we can develop much better methods of prevention, but people will still get sick. So, do I think what we’re doing is promising? Absolutely. Will you have a spray tomorrow? Absolutely not.”
Photo of Debora Foster courtesy Ryerson University© Food Safety News